Heretofore, surgically implantable prosthetic joints, together with tendon and ligament substitutes have been subjected to undesirable localized stress or lacerations and tearing caused by contact with sharp, irregular edges of bone growth on the surface of resected bone. This has often resulted in poor durability and performance of these implants. The present invention relates to a method of minimizing the deleterious effects of spurious bone growth adjacent surgically implanted prosthetic or biprosthetic implants.
Injury to weight-bearing ligaments such as the cruciate ligaments of the knee can occur, either as an isolated injury, or in combination with other ligament injuries of the knee. Damaged or torn cruciate ligaments can be repaired, reconstructed or treated nonoperatively depending upon the extent of the injury, the amount of functional or clinical laxity, the age of the patient, and the activity level desired. Simple repair of the injured ligament involves suturing, and because the cruciate ligaments are poorly vascularized, simple repair is generally insufficient. Reconstruction generally involves the utilization of synthetic ligament substitutes or autologous tissue within the knee joint similar to the cruciate ligament, such as in intraarticular reconstruction, or utilization of autologous tissue outside of the knee joint to strengthen the anterior or anterior lateral rotational stability, such as in extraarticular reconstruction.
Intraarticular reconstruction of anterior and posterior cruciate ligaments of the knee generally involves drilling holes through the tibia and femur followed by insertion of a ligament substitute such as patellar tendon, fascia, and the like through the central channel, and stapling of the ligament substitute to the outer surface of the bone adjacent the resected channel. The most common mode of failure is generally observed at the place where the ligament is subjected to stress; at the site where the ligament substitute enters or exits from the tibia or femur. Ordinarily the bone grows around and into the implanted ligament during the healing process leaving high stress concentrations at these exit sites. Moreover, the ingrowth of resected bone into the ligament implant throughout the length of the resected bone channel, which immobilizes the implant by restricting its naturally intended gliding motion and reducing its flexibility, may damage the implant due to sharp, jagged, irregular bone edges formed during the healing process.
Various attempts to improve the durability, compatibility, and mechanical functioning of naturally occurring and prosthetic tendons and ligaments have only been marginally successful. Such remedies include covering the ligament substitute with a vitreous carbon coating; plastic sheaths made of polyethylene, silicone rubber, and the like; silicone rubber-reinforced Dacron mesh sleeves; woven meshes of synthetic plastic fibers; stainless steel sleeves; metal wire meshes; and the like. Heretofore, implantable ligament substitutes in close proximity with resected bone have suffered the effects of irregular bone formation, high stress levels, and marginal durability.
Rheumatoid arthritis is an inflammatory disease of the soft tissues that causes severs destruction of the joint tissues. Inter alia, the disease weakens the capsule and ligament of the joint, causing the fingers to become displaced. Prior to the advent of implant arthroplasty of these joints, resection arthroplasty and a procedure known as fusion were the only alternatives to either relieve pain and to restore functional range of motion to the affected areas. Resection arthroplasty merely removed the joint capsule which allowed the space to fill in with a new surface of fibrous tissue, providing a false joint. Fusion caused a bond union across the joint, provided stability and relief of pain, but did not allow for motion in the fused joint. Implant resection arthroplasty is a surgical procedure performed to correct finger-joint deformation in patients with severe destruction of joints caused by progressive rheumatoid arthritis. A flexible elastomeric implant, preferably of silicone rubber, is the most commonly used adjunct to this arthroplasty procedure. Examples of such prosthetic joints include those disclosed in U.S. Pat. Nos.: 3,462,765; 3,593,342; 3,681,786; 3,818,513; 3,875,594; 3,879,767; 3,886,600; and 4,178,640.
One of the problems encountered with these flexible implants is crack propogation and susceptibility to stress which ultimately leads to joint implant failure. During the healing processes following bone resection, sharp jagged edges of bone may develop which eventually initiate tears and cracks in the elastomeric implant. Swanson, in U.S. Pat. Nos. 4,158,893 and 4,198,713, has disclosed various protective devices for preventing lacerations or tearing of these flexible implants due to the damaging effects of the spur bone formation of the resected bone. In U.S. Pat. No. 4,158,893 the protective device is a sleeve adapted to fit within the intramedullary canal, wherein the sleeve is made of medical grade material such as porous polytetrafluoroethylene or high density polyethylene, which permits the bone to grow into its exterior surface. In U.S. Pat. No. 4,198,713, the protective device is a curvilinear shield adapted to conform to the upper portion of the prosthesis outer surface, wherein the shield is made of highly polished stainless steel which permits relative sliding, reciprocating motion between the prosthesis and the protective device.
In spite of the various improvements described hereinabove, the tearing and cracking of these prostheses has persisted. A need therefore exists for a device which interfaces between the flexible implants and the resected bone which not only discourages or inhibits the formation of bone spurs and sharp irregular bone, but promotes a smooth, regular, even remodeling of the resected bone surface and thus provides a smooth edge at this interface. Heretofore, no such device has been available.